For those [observations] that I made in Leipzig in my youth and up to my 21st year, I usually call childish and of doubtful value. Those that I took later until my 28th year [i.e., until 1574] I call juvenile and fairly serviceable. The third group, however, which I made at Uraniborg during approximately the last 21 years with the greatest care and with very accurate instruments at a more mature age, until I was fifty years of age, those I call the observations of my manhood, completely valid and absolutely certain, and this is my opinion of them.

It was not just the Church that resisted the heliocentrism of Copernicus.

When I had satisfied myself that no star of that kind had ever shone before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes.

The body of the Earth, large, sluggish and inapt for motion, is not to be disturbed by movement (especially three movements), any more than the Aetherial Lights [stars] are to be shifted, so that such ideas are opposed both to physical principles and to the authority of the Holy Writ which many time: confirms the stability of the Earth (as we shall discuss more fully elsewhere).

That the machine of Heaven is not a hard and impervious body full of various real spheres, as up to now has been believed by most people. It will be proved that it extends everywhere, most fluid and simple, and nowhere presents obstacles as was formerly held, the circuits of the Planets being wholly free and without the labour and whirling round of any real spheres at all, being divinely governed under a given law.

And when statesman or others worry [the scientist] too much, then he should leave with his possessions.

So mathematical truth prefers simple words since the language of truth is itself simple.